A wind turbine, a wind turbine controller, and a method for controlling a wind turbine are disclosed herein. In particular, the wind turbine, the wind turbine controller, and the method for controlling the wind turbine described herein are adapted to take rotor blade stall into account.
By means of their rotor blades, wind turbines capture kinetic energy from wind and convert it into rotational energy of a rotor shaft. Typically, this rotational energy is used to drive an electric generator, either directly or via a gear box. The amount of power extracted from the wind depends, inter alia, on the aerodynamic angle of attack between the rotor blade nose and the incoming air flow. If, for a given wind speed, a certain maximum angle of attack is exceeded, the flow separates at the rotor blades' surface and vortices form at the blade. This effect is known as stall and limits the aerodynamic power capture. Furthermore, stall may increase the noise generated by the wind turbine which might be a problem, e.g. when the turbine site is located near residential areas and particularly during nighttimes.